The invention concerns balloon dilatation catheters and, particularly, to balloon dilatation catheters of the type used in percutaneous transluminal coronary angioplasty (PTCA) in which a stenosed region of a coronary artery is dilated to increase the blood flow through that artery. The PTCA procedure typically involves advancement of a guide catheter from a percutaneous puncture in the femoral or brachial artery to place the distal end of the guide catheter at the entrance to the coronary arteries. With the guide catheter positioned, a balloon dilatation catheter is passed through the guide catheter into the coronary arteries. The balloon dilatation catheter typically is used in conjunction with a small diameter steerable guidewire which can be manipulated into the selected arterial branch to be treated. After the guidewire has been manipulated into place, the balloon catheter is advanced, with the balloon in a deflated state, over the guidewire into the stenosis. The balloon then is inflated to dilate the artery.
Early PTCA catheters used a separate guidewire. The development of improved techniques by physicians, however, lead to attempts to enter and dilate very narrow stenoses. That, in turn, lead to the development of low profile steerable catheters in the form of a balloon mounted directly to and carried by the steerable guidewire. Examples of such catheters are the USCI Probe catheter commercially available from USCI Division of C. R. Bard, Inc., Billerica, Mass. and the Hartzler LPS catheter commercially available from Advanced Cardiovascular Systems, Inc., Mountain View, Calif.
Although angioplasty catheters of the type having a balloon carried directly by the guidewire have met with acceptance, they are not free of difficulty. Among the problems presented by such catheters is that rotation of the steerable guidewire is hampered somewhat because the balloon tends to restrict rotation of the wire. Therefore, although the wire is steerable, it is not always steerable with the facility that may be desired. Another difficulty presented by such catheters is that the balloon or the tubular segment of the catheter proximal of the balloon and to which the balloon is attached may become somewhat bound, particularly when passed through tortuous coronary arteries. As a result, when the guidewire is rotated, the proximal tube and the balloon may become twisted thereby restricting or preventing flow of liquid inflation medium to or from the balloon.
It is among the general objects of the invention to provide an improved catheter incorporating an integral steerable guidewire and carrying a balloon which provides for a high degree of freedom of motion to facilitate manipulation of the guidewire.
It is also among the objects of the invention to provide a catheter having an integral steerable guidewire in which the balloon and the tubular segment to which it is mounted will not tend to adversely twist closed in response to rotation of the guidewire.